Method for inhibiting the staining of articles fabricated from aluminum-coated products



United States Patent METHUD FGR lNHIiiITIiJG THE STAINING 0F ARTiCLES FABRICATED FROM ALUMINUM- COATED PRODUCTS Richard A. Nickola, Bedford Heights, and Thomas F. Shafier, Jn, Fair-field, Ohio, assignors to United States Steel Corporation, a corporation of Delaware No Drawing. Filed Dec. 28, 1965, Ser. No. 517,093

Int. Cl. C23d 7/04 US. Cl. 148-635 1 Claim ABSTRACT OF THE DISCLOSURE Fabricated aluminum-coated products are treated to inhibit atmospheric staining, by heating them in an oxidizing atmosphere to a temperature between 700 and 1100 F. for from 1 hour at the lower temperature to 10 minutes at the higher.

This invention relates to a treatment for articles fabricated from aluminum-coated products which renders them more resistant to staining or discoloration by atmospheric corrosion.

Aluminum-coated products are now used in fabricating many articles. Such articles have heretofore exhibited a tendency to rather rapid discoloration resulting from the formation of a brown stain on the surface when exposed to the atmosphere. While the stain does not reduce the useful life of the article, it does detract from the appearance thereof. The stain appears to be the result of oxidation of iron at the bottom of microscopic cracks, fissures and pores opened up in the coating on cold-working of the coated product incident to fabrication.

We have invented a novel method of treating articles fabricated from aluminum-coated products, i.e., wire rod, tube or sheet, whereby the tendency to staining on exposure to the atmosphere is materially reduced. In a preferred practice of the invention, we subject fabricated articles in an oxidizing atmosphere such as air, to a temperature between 700 and 1100 F. for a period of from 1 hour or less at the lower temperature to 10 minutes or more at the higher temperature.

The treatment may be effected most conveniently by simply placing the articles, for the appropriate time, in a furnace with an oxidizing atmosphere, heated to the temperature selected. As a specific example, wire buttons were placed for minutes in a furnace or oven heated to 800 F., having air as its atmosphere. These buttons are test samples formed by bending aluminumcoated wire back on itself and winding one end around the remainder for 20 turns. Exposure of the buttons to the atmosphere after the treatment revealed that staining thereof did not occur Whereas early and noticeable staining was observed in the case of untreated buttons.

The effect of our post-fabrication treatment appears to be the oxidation of iron at points where it is exposed by the cracks, fissures, etc., opened up by cold working in fabrication. This oxidation forms magnetite which effectively plugs the surface imperfections, sealing them against subsequent ingress of oxidizing media. Buttons heated as described but under non-oxidizing conditions, i.e., a vacuum or an atmosphere of cracked ammonia gas, do not exhibit the resistance to discoloration resulting from the treatment of our invention.

It will be appreciated that buttons, made as explained above are the samples conventionally used to test the adherence of the coating under an extreme condition of cold Work. Most fabricated articles are subjected only to a much milder degree of cold work and therefore less likely to exhibit staining. Such fractures as may occur in the coating, however, are nevertheless effectively sealed by our treatment with a reduction in the degree of staining compared to that occurring in articles not treated.

Although we have disclosed herein the preferred practice of our invention, we intend to cover as well any change or modification therein which may be made Without departing from the spirit and scope of the invention.

We claim:

1. A method of making products fabricated from aluminum-coated iron-containing material comprising subjecting the material to fabrication to form the products, thereby causing microscopic cracks to open in the surface of the material, then heating the fabricated articles in an oxidizing atmosphere to a temperature of from 700 to 1100 F. for a period of time from an hour to ten minutes, thereby forming magnetite at the bottoms of said cracks and plugging them against further contact with oxidizing media.

References Cited UNITED STATES PATENTS 1,335,024 3/1920 Peschko 1486.3 X 1,409,017 3/1922 Ortiz.

2,167,701 8/1939 Whitfield et a1. -148 6.3 2,421,719 6/1947 Simmons 1486.3 X 2,887,419 5/1959 Baer et a1. l486 .35 3,305,384 2/1967 Kenderi 117 -114 X RALPH S. KENDALL, Primary Examiner US. Cl. X.R. 72-47; 117-131 

